Pretty much as the title says; it'd be nice if we had some kind of configurable retry delay when rsync encounters a vanished file/folder. This would be especially useful in cases involving mounted remote volumes, as it would mean rsync could instead pause and try again in cases where the mounted volume is temporarily disconnected.
Just wanted to add that it may make sense to separate the retry somehow so that folders can be retried while files are skipped, for example, as backups of an in-use hierarchy will be more likely to encounter files that vanish rather than entire directories, so it may be worthwhile skipping the retry delay for files in such cases.